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issue: April 2006 APPLIANCE Magazine

Refrigeration Systems & Compressor Technology
Beyond 13 SEER


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by David Simpson, Contributing Editor

Energy efficiency standards like SEER 13 and upcoming refrigerant changes keep refrigeration systems makers and suppliers busy.

Residential air-conditioner makers in the U.S. now produce models that meet minimum standards of 13 SEER, up from
10 SEER. The benefits in terms of reduced national energy use will eventually be substantial, and individual users will have more energy-efficient, if more costly, models. For the industry, the challenge of meeting the standard was significant.

“Thirteen SEER applications are not new, only the requirement for 13 SEER minimum is new,” points out Scott Hix, vice president, product engineering, Bristol Compressors, Inc. (Bristol, Virginia, U.S.). “Our customers have been producing 13 SEER+ for a long while, though these systems have been mostly a niche or ‘sell-up’ product with minimal volume. So the real challenge was not to get 13 SEER but to do it cost-effectively and keep 13 SEER affordable. They have done this through larger coil surface, improved heat transfer surfaces and fin design, modifications to fan blades/speed and airflow characteristics, and use of higher efficiency compressors. Also, the higher minimum SEER is driving a higher usage of thermostatic expansion valves than was the case with 10 SEER minimums.”

Why thermostatic expansion valves? In the traditional fixed orifice technology, the size of the orifice is an average that remains constant. Therefore, the flow of refrigerant into the evaporator remains constant, regardless of the cooling demand on the system. Using a thermostatic expansion valve increases efficiency by varying the flow of refrigerant into the system’s evaporator coil, depending on the system load. When the load (the demand for cooling) decreases, the expansion valve orifice partially closes in response. This means less work for the compressor and less energy is consumed.

How easy is it to add a thermostatic expansion valve to a refrigeration system?

“Whenever an equipment manufacturer decides to redesign an existing piece of equipment, or design a new piece of equipment, it is a pretty involved task,” observes Dave Demma, supermarket sales manager, Refrigeration & Air Conditioning – Climate & Industrial Controls Division, Parker Hannifin Corporation (Cleveland, Ohio, U.S.). “First, they will decide on some design criteria, and then search out components to fill the design criteria. They then build a prototype piece of equipment, and test it against the SEER conditions in the lab. This requires manpower and a lot of time. So, it’s not an easy process.”

Still, says Stephen Gugliotta, sales director, air-conditioning, Americas, Danfoss (Baltimore, Maryland, U.S.). “OEMs had a time crunch, and thermostatic expansion valves stood out. Upfront costs were not as high as other alternatives.

“Some OEMs are currently turning their attention towards using electronics, such as variable speed for fans or compressors, or electronic expansion valves,” Gugliotta adds. “The problem here is initial cost. Still, I expect electronics to be in 10 percent to 20 percent of U.S. residential air-conditioning within 5 to 6 years. This will be driven by increased interest in energy efficiency and more cost-effective electronic solutions.”

Increasingly stringent food safety regulations are spurring the trend toward electronic step-motor controls for refrigerant flow controls. Electronic valves, like the CDS evaporator pressure regulating valve from Sporlan Division – Parker Hannifin (Cleveland, Ohio, U.S.), offer extremely precise and accurate control, and the valves can be interfaced with Sporlan or third party controllers.

Step-Motor Valves

Others, including Parker Hannifin’s Demma, also anticipate increased electronics content in refrigeration systems. For instance, he says, “We are seeing more interest in electronically controlled step-motor expansion valves (EEVs). They offer better control, especially at lower load conditions. A conventional mechanical expansion valve will throttle to perhaps 40 percent of its nominal capacity and still maintain correct superheat. An EEV will throttle to perhaps 5 percent of its nominal capacity. And it is easily adjustable. It simply requires dialing in a set-point at the controller.”

In fact, his company is seeing increased interest in all step-motor valves, particularly electronically controlled suction line regulators (CDS) in supermarket refrigeration applications. “They are replacing conventional EPR valves (evaporator pressure regulators) as a means of fixture temperature control. EPR valves will do this by maintaining a constant evaporator pressure at the fixture. This guarantees that the refrigerant boils at a constant temperature in the evaporator, which results in a fairly constant discharge air temperature. The CDS valve utilizes a step-motor with over 6,000 steps from fully open to fully closed (for all intents this could be considered infinite steps of modulation), and it responds to discharge air temperature. They are able to maintain temperatures in the range of +/- 0.5°F. They are very repeatable, and extremely reliable. Because they control temperature, there is never a need for readjustment due to seasonal or load changes.”

The X Range compressor line from ACC Compressors (Barcelona, Spain) includes more than 20 models ranging from 16 to 23 cc. The compressors can work with HFC refrigerant gases, such as R-134a, R-404A and R-507. The compressors are designed to minimize the acoustic level and they incorporate a high-performance electrical motor and a bottom-supported suspension system to minimize vibrations.

Speed Choices

In today’s market, one solution may not be enough to satisfy customer needs. Subodh Sharma, senior product manager for Heatcraft Refrigeration Products LLC (Stone Mountain, Georgia, U.S.), reports that his company talked to 25 of its largest customers, and others, about their priorities for air-cooled condensers. These are typically used for heat rejection in applications such as supermarkets, telecom or process cooling. The company found four main areas of customer priority—low noise and energy efficiency, higher capacities in a smaller footprint, serviceability, and affordability. Some customers emphasized some areas far more than others.

“In the past, when we launched a product, we tended to make a design that we thought most customers would need. But our research made clear to us that we have customers with different needs and priorities,” Sharma says. “There are some who are willing to pay a premium to meet their sound requirements, or to have energy efficiency. On the other hand, some customers, typically in process cooling, were most concerned with effective heat removal.”

With this in mind, Heatcraft developed new condenser lines for its Bohn, Larkin, Climate Control, and Chandler brands. All the condensers feature better sound and energy levels, and offer easier serviceability than their predecessors. The Bohn brand Ambassador series of air-cooled condensers uses 540 rpm or 830 rpm motors, rather than the more common 1,140-rpm motors. “The lower rpm translates to better efficiency and lower noise in a smaller footprint,” explains Sharma. “We designed different forward-swept fan blades for each motor, which optimize aerodynamics for a quieter, more efficient operation. Also, we included QuietEdge fan technology, from our Lennox parent company, on the blades’ trailing edges. This adds turbulence to the airflow, which helps to reduce the sound. Our noise level tests at 49.5 db on a 540 rpm motor, compared to
54 db on an older model.”

To meet the needs of customers who give priority to quiet operation and efficiency, the company introduced the Monarch Series, using an electronically commutated (EC) motor. “It’s the first time this technology, which is common in Europe and Asia, has been used for condensers in the U.S.,” says Sharma. “Airflow varies between about 200 rpm to 1,100 rpm, depending on capacity needs. For the customer, the motor and controls are self-contained so need no additional maintenance. Because the motor can operate up to 1,100 rpm, it’s got higher capacity, and the customer may need fewer fan cells. Typical operating speeds are much lower.”

In a move to improve its frozen beverage dispensers, Lancer FBD (San Antonio, Texas, U.S.) redesigned its models to use scroll rather than reciprocating compressors. The company says the scroll compressors, supplied by Emerson Climate Technologies (Sidney, Ohio, U.S.), will be more reliable. This is largely due to fewer moving parts and being rated at twice the number of starts. In the case of the four-barrel model 564 shown, the company replaced two compressors with a single scroll compressor. The new scroll refrigeration system makes possible lower power consumption (approximately 50 percent less than a two-compressor system), reduced wiring installation costs (30 A rather than 50 A), and easier access for servicing due to smaller compressor size. Another significant advantage is that width is reduced to 26 inches, so the dispenser needs several inches less space than other models.

Commercial Legislation

Commercial units such as reach-in freezers are now coming under more scrutiny because of their impact on electricity usage. According to a white paper from Emerson Climate Technologies (Sidney, Ohio, U.S.), The State of Energy-Consumption Legislation for Commercial Refrigeration Applications, annual electricity consumption by the commercial sector in the U.S. grew by 229 percent from 1970 to 2000, at a time the population grew 38 percent.

A major concern is that several states are implementing their own energy standards. In order to avoid a patchwork of state regulations, the Air-Conditioning and Refrigeration Institute (ARI) proposed the federal government nationalize energy-consumption standards for commercial reach-in refrigerators and freezers. The effective date recommended in this proposal was January 2010, with the final energy-consumption standards equal to both an Energy Star voluntary proposal and final standards from the California Energy Commission. These recommendations were enacted in the Energy Policy Act of 2005.

Some states are also implementing legislation to limit the allowable energy consumption of commercial ice-cream freezers, vending machines, ice machines, and walk-in refrigerators and freezers. One possible forthcoming response from ARI might be a proposal for national ice machine standards.

“The white paper looks at what can be a confusing situation,” reports Leland Smith, foodservice and transport market manager for Emerson’s Copeland Corporation (Sidney, Ohio, U.S.). “We are hoping people can use the paper as a framework for understanding and making appropriate decisions at the OEM level.”

Modine Manufacturing Company (Racine, Wisconsin, U.S.) received a Cooling Innovation Award for its PF2 micro channel product line at the 2006 AHR Expo. The Parallel Flow Plate Fin (PF2) cooling core technology is an all-aluminum, brazed heat exchanger designed to solve water drainage problems found in some micro channel heat exchangers. The fin design can drain water in vertical or horizontal settings. It can be applied in condenser and evaporator applications in refrigeration and air-conditioning systems. The company reports the technology allows OEM engineers to save cost, decrease weight or reduce refrigerant charge.

Refrigerants in Transition

The industry has selected its refrigerants over the years by weighing the thermodynamic advantages of the various substances and other factors such as chemical stability, toxicity, cost, and compatibility with other elements of the cooling system, like materials and lubricants. However, choices are also being constrained by various mandated or proposed restrictions on refrigerants because of environmental issues. One such restriction takes effect in just 4 years. This is the elimination of hydrochlorofluorocarbon (HCFC) refrigerants—predominantly R-22—for new equipment in developed countries.

The goal is to eventually remove chlorine from all new refrigeration systems, and thus cut refrigerant ozone depletion potential (ODP). In the EU and China, domestic refrigerator makers removed chlorine by using hydrocarbon (HC) refrigerants such as isobutane. However, the largest HCFC alternative, at least for the time being, will be hydrofluorocarbons (HFCs). Already, many refrigeration systems have been switched to HFCs.

According to Danfoss, HFCs allow equipment to operate with more energy efficiency than any alternative available for residential air-conditioning and commercial uses. At present, components exist and can be supplied in manufacturing quantities for systems using HFCs. This is not the case with some other alternatives. HFCs are less harmful to the environment than chlorofluorocarbons (CFCs) and HCFCs. They are more quickly depleted in the atmosphere, and so have less global warming effect.

“With the deadline approaching for R-22 in new equipment, we are seeing a lot of confusion about which refrigerants are the best replacements in commercial appliances,” observes Tim Uderman, applications engineer at Emerson Climate Technologies. “There has been a gap in the industry in explaining what is going on. To address this, we have published a white paper, Refrigerants for Commercial Refrigeration Applications.

“This paper is an effort to be objective, and to help in the discussion about alternatives,” says Uderman. “There really hasn’t been much discussion until recently, and now everyone is scrambling to try to get things done in time. One factor delaying action has been the 13 SEER deadline earlier this year, which put the topic of R-22 replacement on the back burner for a lot of residential air-conditioner companies.”

Looking at compressor selection, says Bristol Compressor’s Hix, “At least for R-22, we believe that a lowest total applied cost strategy will drive the larger tonnage systems (greater than about 3.5 tons) to scroll technology. Reciprocating compressors will remain the lowest applied cost alternative below 3 tons.”

Hix says the company has been making compressors for use with R-410A since 1995. Bristol, he said, “Will continue to focus on total applied cost as the measure for our product strategy plans. It may be that R-410A drives us to a different product strategy. We will have both reciprocating and scroll products available to meet these requirements just as with R-22. OEMs that are making the switch will have to focus on product cost and education of the service end of the business.”

Refrigeration system producers should be aware that U.S. demand for R-22 is expected to increase significantly in 2006. “Based on our interactions with many OEMs, it appears that most plan to achieve the new 13 SEER requirement via equipment modifications resulting in a larger R-22 charge size per unit,” says an October 2005 report from DuPont Refrigerants (Wilmington, Delaware, U.S.). “As a result, we estimate total R-22 requirements for the U.S. stationary OEM segment will increase 25 to 35 percent in 2006.”

The company points out that, at the same time, there will be limited U.S. availability in the next few years. A January 2003 EPA regulation limits the amount of R-22 that can be produced and/or imported into the U.S. Despite the rapid introduction of equipment designed to use HFC refrigerants, R-22 is still, by far, the largest volume refrigerant used in the stationary air conditioning and refrigeration segments.

Besides a supply and demand imbalance, other factors are helping drive up costs, DuPont notes. Prices for key raw materials (chlorocarbons and fluorspar to make hydrofluoric acid) have increased significantly over the past 2 years and are forecast to increase again in 2006. Energy costs in R-22 manufacturing facilities have jumped, as have steel costs for cylinders, and fuel and trucking costs to transport the products. The bottom line for 2006-07, reports the chemical company, is fixed supply, increasing demand, and much higher costs.

“The industry will continue efforts to develop environmentally friendly products aimed at protecting the ozone layer and preventing global warming,” predicts Jik-Soo Kim, manager, Integrated Marketing Communication Group, Digital Appliance Company, LG Electronics (Seoul, South Korea). His company makes refrigeration system components including reciprocating/rotary/scroll/linear compressors for its own products and other air-conditioner and refrigerator manufacturers. “Thus, hydrocarbon or HC mixture types will likely lead refrigerants in the future. Additionally, major refrigerant makers will work to develop innovative zero Global Warming Potential (GWP) refrigerants.

“Regarding the oil problem, since oil’s compatibility with refrigerants is a key issue, oil will be in line with the refrigerant trends. Appliance makers will look to develop highly efficient oil using nanotechnologies. Therefore, any big changes in refrigeration systems will be in conjunction with changes in refrigerants and oil. As changes in refrigerants, oil, and others will bring about chemical pressure and temperature changes, new designs will be incorporated to respond to physical changes.”

Look for the industry to keep busy with new designs, materials, and technologies to meet the evolving worldwide needs in refrigeration systems.

Also read, Refrigeration Systems & Compressor Technology:
Rigid Insulation, Flexible Formulas

 

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